ASTM G_Laboratory Immersion Corrosion Testing of Metals – Free download as PDF File .pdf), Text File .txt) or read online for free. ASTM G Other ASTM procedures for laboratory corrosion tests are tabulated in the Appendix. NOTE 1—Warning: In many cases the corrosion product on the reac-. ASTM G Standard Practice for Laboratory Immersion Corrosion Testing of Metals_能源/化工_工程科技_专业资料. 暂无评价|0人阅读|0次.
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A number in parentheses indicates the year of last reapproval. A superscript epsilon e indicates an editorial change since the last revision or reapproval. These factors include specimen preparation, apparatus, test conditions, methods of cleaning specimens, evaluation of results, and calculation and reporting of corrosion rates.
This practice also emphasizes the importance of recording all pertinent data and provides a checklist for reporting test data. Warning—In many cases the corrosion product on the reactive metals titanium and zirconium is a hard and tightly bonded oxide that de? In many such cases, corrosion rates are established by mass gain rather than mass loss.
The values given in parentheses are for information only. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.
This practice, rather than a standardized procedure, is presented as a guide so that some of the pitfalls of such testing may be avoided. It is impractical to propose an in? For proper interpretation of the results obtained, the speci?
Current edition approved May 1, Originally approved in Last previous edition approved in as G 31 — 72 Alternatively, the coupon may be rotated through the environment, although it is then difficult to evaluate the velocity quantitatively because of the stirring effects incurred. If this is a factor to be considered in a speci? The amount of possible contamination can be estimated from the loss in mass of the specimen, with proper application of the expected relationships among 1 the area of corroding surface, 2 the mass of the chemical product handled, and 3 the duration of contact of a unit of mass of the chemical product with the corroding surface.
For example, the accumulation of cupric ions in the testing of copper alloys in intermediate strengths of sulfuric acid will accelerate the corrosion of copper alloys, as compared to the rates that would be obtained if the corrosion products were continually removed. Cupric ions may also exhibit a passivating effect upon stainless steel coupons exposed at the same time.
In practice, only alloys of the same general type should be exposed in the testing apparatus. There are a number of other special types of phenomena of which one must be aware in the design and interpretation of corrosion tests. The behavior of the specimens in this galvanic couple are compared with that of insulated specimens exposed on the same holder and the galvanic effects noted. It should be observed, however, that galvanic corrosion can be greatly affected by the area ratios of the respective metals, the distance between the metals and the resistivity of the electrolyte.
Gg31 coupling of corrosion coupons then yields only qualitative results, as a particular coupon re?
It is necessary to evaluate this localized corrosion separately from the overall mass loss. Close attention and a more sophisticated evaluation than a simple mass loss measurement are required to detect this phenomenon.
This cannot be evaluated by mass loss alone. The reporting of nonuniform corrosion is discussed below. It should be appreciated that pitting is a statistical phenomenon and that the incidence of pitting may be directly related to the area of metal exposed.
For example, a small coupon is not as prone to exhibit pitting as a large one and it is possible to miss the phenomenon altogether in the corrosion testing of certain alloys, such as the AISI Type series stainless steels in chloride contaminated environments.
This cracking occurs under conditions of applied or residual tensile stress, and it may or may not be visible to the unaided eye or upon casual inspection. A metallographic examination may con? It is imperative to note that this usually occurs with no signi? Generally, if cracking satm observed on the coupon, it can be taken as positive indication of susceptibility, whereas failure to effect this phenomenon simply means that it did not occur under the duration and speci? Separate and special techniques are employed asgm the speci?
If agitation is required, the apparatus can be modi? The suggested apparatus is basic and the apparatus is f31 only by the judgment and ingenuity of the investigator. For solutions corrosive to glass, suitable metallic or plastic kettles may be employed.
A large surface-to-mass ratio and a small ratio of edge area to total area are desirable. These ratios can be achieved through the use of square or circular specimens of minimum thickness. Masking may also be used to achieve the desired area ratios but may cause crevice corrosion problems. Circular specimens should preferably be cut from sheet and not bar stock, to minimize the exposed end grain. Special coupons for example, sections of welded tubing may be employed for speci?
With a thickness of approximately 3 mm 0. The total surface area of a circular specimen is given by the following equation: Occasional exceptions, in which a large difference is observed, can occur under aetm of borderline passivity of g1 or alloys that depend on a passive? Ast, at least duplicate specimens should normally be exposed in each test.
The mechanical property commonly used for comparison is astj tensile strength. Measurement of percent elongation is a useful index of embrittlement. The procedures for determining these values are shown in detail g1 Test Methods E 8. This can be done by chemical treatment picklingelectrolytic removal, or by grinding with a coarse abrasive asm or cloth such astmm No.
If clad alloy specimens are to be used, special attention must be given to ensure that excessive metal is not removed. In special cases for example, for aluminum and certain copper alloysa minimum of 24 h storage in a desiccator is recommended. The choice of a speci? A commercial surface may sometimes yield the most signi? Too much surface preparation may remove segregated elements, surface contamination, and so forth, and therefore not be representative.
It may be desirable to test a surface representative of the material and metallurgical conditions used in practice. If metallic contamination of the stamped area may in? However, the absence of cracking should not be interpreted as indicating resistance see 4. This resurfacing may cause some surface work hardening, to an extent which will be determined by the vigor of the surfacing operation, but is not ordinarily signi?
For relatively soft metals such as aluminum, magnesium, and copperscrubbing with abrasive powder is not always needed and can mar the surface of the specimen. Proper ultrasonic procedures are an acceptable alternate.
The use of towels for drying may introduce an error through contamination of the specimens with grease or lint. If cleaning deposits for example, scouring powder remain or g331 of complete dryness is suspected, then recleaning and drying is performed until a constant mass is attained.
These factors include oxygen concentration, temperature, rate of? Molarity and normality are also helpful in de? Preferably, the use of a re?
These changes should be determined if possible. Where required, the exhausted constituents should be added or a fresh solution provided during the course of the test. Most tests related to process equipment should be run with the natural atmosphere inherent in the process, such as the vapors of the boiling liquid. Extraneous effects can be encountered if the air stream impinges on the specimens.
A liquid atmospheric seal is required on the test vessel to prevent further contamination. For other degrees of aeration, the solution should be sparaged with air or synthetic mixtures of air or oxygen with an inert gas. Oxygen saturation is a function of the partial pressure of oxygen in the gas.
The actual time of contact of the metal with the solution must also be taken into account. Any necessary distortion of the test conditions must be considered when interpreting the results. If clad alloys are exposed, special procedures will be required to ensure that only the cladding is exposed, unless the purpose is to test the ability of the cladding to protect cut edges in the test solution. Other procedures that require the removal of solid corrosion products between exposure periods will not measure accurately the normal changes of corrosion with time.
However, there are cases where this assumption is not valid. For example, lead exposed to sulfuric acid corrodes at an extremely high rate at? The phenomenon of forming a protective?
ASTM NACE / ASTMG31 – 12a Standard Guide for Laboratory Immersion Corrosion Testing of Metals
Therefore, short tests on such materials would indicate a high corrosion rate and be completely misleading. With borderline conditions, a prolonged test may asgm needed to permit breakdown of the passive?
Consequently, tests run for long periods are considerably more realistic than those conducted for short durations. This statement must be quali? Methods of Cleaning Specimens after Test 9. Location of deposits, variations in types of deposits, or variations in corrosion products are extremely important in evaluating localized corrosion, such as pitting and concentration cell attack.
Scrubbing with a bristle brush and mild abrasive is the most popular of these methods. The others are used principally as a supplement to remove heavily encrusted corrosion products before scrubbing. Care should be used to avoid the removal of sound metal. Solvents such as acetone, carbon tetrachloride, and alcohol are used to remove oil, grease, or resin and are usually applied prior to other methods of cleaning.
Chemicals are chosen for application to a speci? Methods for chemical cleaning after testing of speci? A method of electrolytic cleaning is described in Practice G 1. Careful observation is needed to ensure that pitting does not occur during cleaning.
Interpretation of Results asttm The mass loss during the test period can be used as the principal measure of corrosion. Duplicate strips of low-carbon steel, each 19 by 76 mm 3? The most common testing periods are 48 to h 2 to 7 days.